A “region lock” is I/O synchronization which prevents data integrity issues in a Redundant Array of Independent Disk (RAID) data storage system by preventing multiple initiators (or other execution entities, such as threads) from simultaneously accessing a particular RAID logical volume in the storage system. In a “multi-initiator” RAID storage system, each initiator maintains a local Input/Output (I/O) cache and a region lock management structure. Each region lock generally includes a data structure within the initiator to maintain a list of locked and unlocked regions in all individual RAID logical volumes and grants its initiator a “lock” to a region of a RAID logical volume when the region becomes available such that the initiator may perform I/O operations thereto. In existing methods, initiators are separated from each other by an inter-server connection. Because initiators maintain their own region locking data, the region locks become desynchronized and potentially corrupt data in the storage system which is common to multiple initiators. Cache coherency is also at risk in such a multi-initiator system.